Adolescent substance use remains a significant public health issue due to the short- and long-term physical and social consequences related to use. Research has shown that pubertal timing, when adolescents begin pubertal development relative to their peers, may lead to adolescent substance use. However, it is not clear why pubertal timing may lead to substance use. The proposed research will examine the relationship between pubertal timing and the development of substance use by testing two competing hypotheses: the maturational-deviance and early-maturational hypotheses. The specific aims of the study are: 1) To compare the maturational-deviance and early-maturation hypotheses by determining the relationship between self-reported pubertal timing at age 11 and the development of substance use (i.e., cigarettes, alcohol, and marijuana) through age 17; 2) Following the maturational-deviance hypothesis, to determine whether psychological variables (i.e., body satisfaction, anxiety, depression, and sensation seeking) mediate the relationship between pubertal timing and the development of substance use; and 3) Following the earlyrinaturation hypothesis, to determine whether social variables (i.e., close friends' pubertal development and close friends' substance use) mediate the relationship between pubertal timing and the development of substance use. The proposed research will conduct a secondary analysis of de-identified data from the Context of Adolescent Substance Use study (R01 DA13459), a longitudinal study of three sequential cohorts of adolescents in grades 6-8 at baseline (n=5,220). The primary analytic approach used in the proposed research will be longitudinal growth modeling (LGM). If pubertal timing does impact adolescent substance use, it is crucial to determine the mediators of this relationship. The timing of pubertal onset cannot be altered but we can design interventions to impact psychological or social factors that may lead to the decline of adolescent substance use. These interventions can then be targeted to those most at risk for substance use based on their pubertal timing in order to delay and slow the development of substance use among adolescents. [unreadable] [unreadable] [unreadable]